The Aqua Medic Helix Max 5 Watt UV Sterilizer uses an aggressive spiraling flow design that incorporates more "twists" in a single pass through the housing. This increase in contact time means big gains in efficiency. The 5 Watt Helix Max is appropriate for aquariums from 10 to 75 gallons. A pump is needed for the sterilizer. The flow rate through the sterilizer must be between 50 and 100 gph.